Advancement of GNSS

Advancement of GNSS and Their Affect on Field Of Land Surveying

Advancement of GNSS and Their Affect on Field Of Land Surveying

Introduction

GNSS or Global Navigation Satellite Systems is the standard generic terms used for satellite navigation systems that give independent ge0-spatial positioning with global coverage (Liu et.al, 2009, pp. 2). Global Positioning System

The Global Positioning System or the GPS is a satellite based system through which locations could be identified anywhere round the world. It gives the most reliable positioning, routing and timing. It was made in the 1970s by the U.S defence department. At the beginning, it was solely for the military purposes. Later it became available for the civilians, as well. The GPS system came into its truly functional form in the year 1995 (Fern_andez, 2010, pp. 3-4). It comprises of satellites, receivers and controlling and monitoring stations. GPS receivers capture the information generated by the satellites and uses triangulation to determine the user's accurate location. It provides continuous position and time details irrespective of the weather conditions.

The GPS systems could be used in a number of cases, such as, 1. For knowing the exact position locations like signalling the helicopter pilot with one's exact location to get oneself picked up. 2. It could be used for navigation purposes. For example if one wish to move from one place to another this system could be useful. 3. Digitized maps could be made using GPS system like plotting the fire zones and hot spots. 4. For the determination of distances between two locations again this technique could be handy (Bogens et.al., 2007, pp. 5.1). Working of the Global Positioning System

The working of GPS base on a collection of continuous moving satellites around the earth. Atomic clocks are present in these satellites. They deliver radio signals having helpful information. The transmitted signals look over by the controlling stations. They are received by the GPS receivers. GPS receiver requires input from only three satellites to roughly plot the 2D position. This plotting would not be very exact. For 3D plotting which is more authentic inputs from four or more satellites are essential. Segments of GPS

The GPS comprises of three segments, namely space, control, and user segments.

Source of Image: http://www.nwcg.gov/pms/pubs/475/PMS475_chap5.pdf

Space Segment

This segment is made up of 29 satellites which move around the globe after 12 hours at an altitude of 12,000 miles. The high altitude helps in covering a larger area. The satellites positions in such a manner in their orbits that the GPS receivers could receive signal form a minimum of four satellites at any provided time. These satellites have individual atomic clocks. They generate low frequency radio signals containing distinctive codes. These codes contain two sine waves transformed by two digital codes and a navigation message (Fern_andez, 2010, pp. 3-4). This helps in their recognition by the GPS receivers. These waves or emissions help the GPS receiver in determining the travelling time of the waves from satellite to the ...